Microbial mats are abundant in the small glacial meltwater streams of Antarctica. Despite the limited amount of nitrogen (N) released from source glaciers and the high uptake rates shown by mats, these communities can remain abundant kilometers downstream. Given that there are no other N inputs from the surrounding landscape, how can these mats persist?
In a new paper in Limnology and Oceanography Letters, Tyler and his colleagues from the University of Colorado and Virginia Tech used stable isotopes to show that N released from the source glacier is exhausted after only several hundred meters in two streams with abundant mats. After this point, most or all stream N originates from fixation by the cyanobacterial genus Nostoc, and is likely made available through its mineralization in the underlying hyporheic zone. These results demonstrate the importance of N2 fixation to primary producers growing in nitrogen-limited streams, but also the role of organic matter recycling to meeting nutrient budgets.
Kohler TJ, Stanish LF, Liptzin D, Barrett JE, McKnight DM (2018) Catch and release: Hyporheic retention and mineralization of N‐fixing Nostoc sustains downstream microbial mat biomass in two polar desert streams. Limnology and Oceanography Letters 3:357–364 doi: 10.1002/lol2.10087